The goal of this project is to study three aspects of the processes by which porphyrins may be effective both in location and regressions of tumors: (1)\the aggregation processes of porphyrins in aqueous solutions; (2)\the binding and incorporation of the porphyrins from the aqueous phase into membranes using liposomes as models; and (3)\the possible use of liposomes and of serum proteins (or their interference) as porphyrin delivery systems. The study is aimed at the molecular level. Procedures for studying the effect of porphyrin self-aggregation on porphyrin-albumin binding were developed. For DP both monomer and dimer species were found to bind to the protein, the data fitting best with a model having one high-affinity site for the monomer and one (different) high-affinity site for the dimer. The monomer binding constants determined for HSA and for BSA are 4.5 x 10[unreadable]7[unreadable] M[unreadable]-1[unreadable] and 1.7 x 10[unreadable]6[unreadable] M[unreadable]-1[unreadable], respectively. The dimer binding constants detrmined for HSA and for BSA are 8 x 10[unreadable]8[unreadable] M[unreadable]-1[unreadable] and l2 x 10[unreadable]7[unreadable] M[unreadable]-1[unreadable], respectively. The binding of DP monomers to HSA was found to be temperature-independent over the range of 22 -\37 degrees C, giving (at 37 degrees C) \G[unreadable]o[unreadable] = -10.8 Kc/mol, \H[unreadable]o[unreadable] = Kc/mol, \S[unreadable]o[unreadable] = +35 e.u., showing the process to be entropy-driven. The binding of DP dimers to HSA was found to be temperature-dependent over the range above, with a continuous nonlinear change in the heat capacity of the system, the binding being entropy-driven in the region of physiological temperature. Zinc-porphyrin was shown to form in HP, HPD, PP and DP solutions containing trace concentrations of Zn, under conditions indicating this species can be part of the drug used in PDT. The metalation fitting first-order kinetics (interpreted to be pseudo) with rate-constants ranging from 0.03-0.10 hours[unreadable]-1[unreadable] (37 degrees C). The dimerization constant of ZnHP at 37 degrees C was determined to be 4.6 x 10[unreadable]4[unreadable] M[unreadable]-1[unreadable], the process entropy-driven at the range of physiological temperature. ZnHP was found to bind to LUV/PC liposomes with a binding constant of 600 M[unreadable]-1[unreadable] (37 degrees C, 2 hrs incubation), the membrane-bound porphyrin monomeric, regardless of the initial state of aggregation in the aqueous phase. (1)